Means for binaural hearing



June 21, 1960 L. HAMMOND 2,942,070

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5AM E A5 ABOVE MEANS FOR BINAURAL HEARING Laurens Hammond, Chicago, JohnM. Hanert, Des Plaines, and Donald R. Kern, Chicago, Ill., as'signors toHammond Organ Company, Chicago, Ill., a corporation of Delaware FiledMar. 26, 1954, Ser. No. 418,865

18 Claims. or. 119-1001 Patented June 21 harmonic analyzer, or like areed type frequency meter, and electrical impulses are transmitted tothe brain cor: responding to the amplitudes of the various frequencieswhich are present in the sounds being heard. The

analyses produced by the two cars, of course, will be the source of thesound, but rather to have the listener 1 perceive the sound asbinaurally omnidirectional; The effect obtained is very unique,possessing to a marked degree the highly desirable property ofmusic'heard in-a' large auditorium, in which all of the sounds reach thelis-' tener by an indefinitely great number of paths. There isapparently no sound heard. through a direct path and therefore there areno positive sensations of definite sound localization. I The inventionmay be employed using any of a variety of sources of electrical tonesignals,such as electric organs and similar electrical musicalinstruments, radio receivers, and various forms of recorded music, suchasmusic recorded on phonograph records, on magnetic wire or tape',.'onfilm, etc.

We have discovered that binaural hearing, or stereophonic perception, islargely caused by the differences in the amplitude analysis of thesound, taken over the audio frequency range, as its reaches thelistener's two cars. If a sound originates at some distance from thelistener it is well-known that violent amplitude distortions, orstanding wave patterns, due to the room's acoustic reflections, will bepresent. The number of upsets or variations in the amplitude response,taken over the audio frequency spectrum, is largely controlled by thedistance and the number of reflectingpaths by which the sound reachesthe, two cars. If it is assumed that the original source of soundisemitting uniform energy'at all the desired signalfrequencies, the carwill not hear-the same energy at all frequencies due to the phaseaddition and cancellation efiects of sounds reaching the ear throughacoustic paths of different lengths. When the source of sound isat adistance which is large in comparison with the wave length of the lowestfrequency being transmitted, cancellations or additions may occur at anyof the frequenciesbeing emitted.

radically different for a sound coming from a distant source because thevarious paths by which the sound reaches the two ears can be radicallydifferent at many different frequencies. Hearing at a distance,therefore,- results in a great number of different amplitude responsesover the'audio frequency spectrum.

If the source is very close, then the analyses by the two cars willclosely coincide and the brain interprets this" as a sound which isrelatively close to the listener. If, on the other hand, the analyses bythe two ears discloses many different and conflicting amplituderesponses, the brain will interpret these many opposing upsets as beingcaused by a source which is relatively distant fromthe eat.

It is well-known in music that the most desirable conditions forpleasurable listening involve relatively long distances like 40 and 50feet, and that it is undesirable to" listen-for instance, to a violin-ina small closet-like enclosure. The apparatus of our invention isdesigned to produce a pleasing illusion of listening in a largeenclosure despite the fact that the actual source of sound is directlyadjacent the listener's ears. The method which we em ploy forcreating'this binaural illusion is to modify the signals occurring atthe two ears in such a way as toproduce many upsets in amplitude overthe audio frequency spectrum in each of a pair of electroacoustictransducers," such as earphones, respectively positioned at the twocars, so thatthe sound emitted by one transducer is heard-predominantlyby one of the listeners ears and that the sound emitted by the othertransducer is heard predominantly bythe other ear of the listener, andfurther, to cause these amplitude variations to occur at diflerentfrequencies for the two earphones. By so doing, we have found that it ispossible to create an amazingly real quality of stereophonic perception,namely, the effect of hearing sound in a large auditorium having idealacoustical properties for listening to music. 1 -When listening with theapparatus of our invention, the

' listener is unable to acknowledge the fact that the sound isoriginating at his ears but rather perceives the phe-- nomena as beingone of hearing many sources of sound remotely located in alarge-auditorium. 'Thus, it is pos sible to createa very satisfyingbinaural perception with any form of music or speech which mayoriginally beer a -monaura l or single channel character .as, forexample, the signals from a radio receiver, a phonograph pickup, or thesignals from an electrical .musical-instru ment. With the apparatus ofour invention, if the source of sound is disconnected from eitherearphone the carat the other phone perceives the source as beingimmediatelyv adjacent that car. If, however, the source is reconnectedso that the sound is present at both ears, then the listener perceivesthe source of sound as. being remotelylocatedlf the source is emitting arandom noise spectrum in suitable harmonic analyzer will disclose, alarge number a of upsets or variations in amplitude response at thevarious-portions of the audio frequency spectrum being analyzed. Flhegreater the distance between the source and the microphone, the greaterwill be the number of these amplitude upsets within the: gamut ,of theaudio spectrum.-.-

I Inbinaural perception-ofsound one judge, ina general way, the distanceof-a' source of sound by means of the two cars. It is a well-knownauditory phenomenon in many parts of a large auditorium-like enclosurewhich physically does not exist but whose dimensions acoustic propertiesare forcefully suggested. 5

The apparatus may be such that although for eachear; consideredindividually, the frequency response upsets might be excessive andundesirable for listeningto music; this is not true when bothearphones-are energized in-the' manner to be described. This ispartly-because that, while the uniformity. of energy over the audio:frequency spectrum is purposely upset in different ways at theearphones,

' the resultant perception, when both earphones are used, is

oneofhigh fidelity in amplitude responsedue to the summation effect inthe brain of the signals received by the two cars. 'Thus, while theamplitude upsets are iiiten that each of the ears functions in a mannersimilar toja tionally provided for the purpose of achieving a stereophonic acoustic perception they are not present in the final compositeacoustic perception which is due to hearing with both ears.

For example, the apparatus of this invention is intentionally effectiveto attenuate a certain frequency in one car while either statistically,or by inherent circuitry. to make this signal present in the other carthus insuring its presence in the final composite signal due to thecontributions made by both ears.

While the apparatus of the invention utilizes a time delay or usesreverberation apparatus for causing amplitude upsets due to the additionof signals having differing phases, such phase shifting apparatus doesnot result in a sequential perception of the sound by the two ears, thatis, the sound appears to start and cease at substantially the sameinstants in both of the listeners ears. This, of course, is highlydesirable from a musical standpoint as it has been found that delayapparatus which introduces the sound in one ear after it has beenintroduced in the other car is highly unsatisfactory and tiring to thelistener. I It is therefore the object of the invention to providemethods and means for greatly improving the pleasure of listening tomonaural music in accordance with the principles above set forth.

Other objects will appear from the following description, referencebeing had to the accompanying draw x in which:

- Fig. l is a schematic wiring and block diagram showing the preferredform of the invention;

Fig. 2 is a similar diagram of'a modified form of the invention;

Fig. 3 is a similar diagram of a further modification of the invention;and

Fig. 4 is a similar diagram of another modification.

Referring to Fig. l, a source 10 of electrical sound signals maycomprise an electric organ, phonograph, radio receiver, or any othersource of sound, particularly music, in the form of an electrical signaland has output terminals 11 and 1-2.

The output terminal 11 of the source is connected to a point of constantpotential, indicated as ground. The' output terminal 12 of this sourceis connected through an adjustable resistor R16 to a reverberationdevice or apparatus 18. The terminal 12 is similarly connected throughan adjustable resistor R17 to a reverberation appnratus 19. The inputcircuits of the reverberation devices are shown as including coils 24and 25 which may be the primaries of input transformers, or may be thevoice coil windings of electroacoustic transducers. 'Ihese coils arerespectively connected between the resistors R16 and R17 and ground.

The outputs of the reveberation devices 18 and 19 are coupled toamplifiers 26 and 27, and the outputs of the letter are coupled tomixers 28 and 29.

The output of the source 10 is also connected to the input of amplifiers30 and 31 and the outputs of the latter are respectively connected tothe mixers 28 and 29. Each, or at least one, of the mixers may beprovided with an adjustable attenuator 32, 33. The output of the mixer28 is connected to one electroacoustic transducer shown as an earphone34 while the output of the mixer 29 is connected to the other transducerearphone 35 of a pair.

The reverberation devices 18 and 19 are preferably of the type shown inthe patent to Laurens Hammond No. 2,230,836, omitting the meansproviding a direct path for the transmission of the signal from thesource to the speaker shown in said patent, namely, omitting thecircuits including the adjustable resistors 24. However, the dcvioes 18and 19 may be any type of apparatus, (acoustic, recording and play-back,etc.) which will convert nonreverberative input signals intoreverberative output sig nlls. The adjustable attenuators 32 and 33 areprovided so thnt suitable compensation may be made when the app-mm: isused by'those whose acuity of hearing of one elf dificrs from that ofthe other.

It will be apparent that each earphone receives a direct signal from thesource in addition to a signal from the source into which reverberativeeffects have been introduced. Due to unavoidable differences in thefrequency response characteristics of the two devices 18 and 19 thesound at the two cars will be different. Certain frequencies will besounded with greater intensity at one ear than at the other. Assumingthat the attenuators 32 and 33 and the mixers 28 and 29 are adjustedproperly for a normal listener, the total energy of the signal suppliedto the two earphones 34 and 35 will be the same but certain frequenciesin the audio range will be of higher amplitude at one earphone and atlower amplitude at the other earphone. The frequency response pattern israndom so that the overall effect on the listener is that he perceivesthe sound as being produced in a large reverberative room in which thesound reaches his ears through a large number of different paths, and inwhich, due to the spaced position of his two eardrums, certainfrequencies are attenuated as heard by one car, while other difierentfrequencies in the sound heard by the other car are attenuated.

Due to the delay introduced by the reverberation 66! I vices, at thecommencement of a tone only the direct signal transmitted through theamplifiers and 31 will be supplied to the earphones 34 and respectively.Then after a very small fraction of a second the rever- 4 berativesignal will be added until, as the tone signal mpplied by the source 10stops, only the reverberative sigmh will be supplied to the earphones.This latter fact also adds to the three dimensional or stereophoniceffect.

The mixers 28 and 29 are preferably provided will manually operablecontrols, in addition to the adjustable resistors R16 and R17, wherebythe ratios of the reverberative relative to the direct signals suppliedto the two earphones may be varied to suit the wishes of the listener.

For the purpose of maintaining bilateral symmetry in the illustration,two amplifiers 30 and 31 are shown. It is apparent that one of theseamplifiers could be omitted and its output supplied to both mixers 28and 29 for providing the direct signal for both earphones.

The objects of the invention may be achieved by utilizing the lesscostly and more simple modified form of the invention shown in Fig. 2.In this form of the inven tion the source 10 has one of its outputterminals connected to ground and its other terminal connected to areverberation apparatus 42 through a potentiometer RM. The other inputterminal of the reverberation apparatus is connected to ground. Theoutput of the apparatus 42 is coupled to an amplifier 46 and the outputof the latter is supplied to the primary of an output transformer 48.The secondary 50 of this transformer has its end terminals connectedrespectively to one terminal of the pair of terminals of earphones 52,53 by conductors 54 and 56 respectively. The other terminals of theearphones are connected to ground. The secondary winding 50 of thetransformer 48 has a center tap 56 which is connected to the slidingcontactor of a voltage divider RS7 which is connected across the outputterminals of the source 10.

A plurality of capacitors CS8 are adapted to be connected cumulativelybetween the conductors 54 and 55 by a rotary switch member 60. When thisswitch member is moved counterclockwise from the position shown in fulllines to the position shown in dotted lines, it makes contact with acontactor 62 forming part of this switch. thereby to connect conductors54 and 55, and thus shunt the reverberative portion of the signal fromthe earphones whenever the binaural eflect is not desired. The ca-'pacitors C58 and switch 60 operate as a tone control to reduce theamplitudes of the higher frequencies.

In this form of the invention the reverberative signal will be heard inthe earphones in opposite polarity so that while the reverberativesignal is adding to the dim signal in one earphone 52, his subtractingfrom the direct signalintheearpbonefi andviceversa. Becausethern is onlyone means for introducing the reverberation effect, the effect of havingdifferent frequency response characteristics in the reverberative tonestransmitted to the two ears is lost during the decay period after thedirect signal ceases, but in steady state the results obtainable by theapparatus of Fig. 2 are quite similar to those obtained by the apparatusshown in Fig. 1. Either the direct or the reverberative signal may besupplied to the earphones in the push-pull manner.

The system shown in Fig. 3 is quite similar to that shown in Fig. 2except that the source of sound comprises a sound record 70 which may bea phonograph divider R76 is connected .to the center tap of an outputtransformer 48. This transformer forms part of an output system whichmaybe the same as that shown in Fig. 2. Similar reference characters havetherefore been applied to corresponding parts and their description willnot be repeated.

A second pickup 78' is coupled to an amplifier 80, the output terminalsof which are connected to the'ends of the primary winding of transformer48. The pickups 72 and 78 are physically'spaced sufiiciently in thedirection of the movement of the soundrecord 70 so that the delayintroduced in the signal picked up by pickup 78 will be in'the order of70 milliseconds, and the pickups are preferably mounted so that theirspacing in the direction ofthe movement of the sound record may bechanged at will to suit, the discriminatory judgment of the listener.Because it is not essential'that either the direct or the delayedsignals supplied to the two earphones be introduced in oppositepolarity, it is possible to accomplish the objects of the invention bythe apparatus shown in Fig. 4. In this form of the invention the signalsfrom the source 90 are supplied in parallel to two devices 91 and 92 forintroducing delay in the signals, with resultant variations in amplituderesponse in the audio frequencyspectrum when the output thereof iscombined with signals transmittcd directly to the earphones.

- The outputs of the devices 91 and 92 are respectively connected to theearphones 93 and 94 through adjustable decoupling impedanoes' R95 andR96, while the signal from the source 90 is transmitted directly totheearphones 93 and 94 through adjustable decoupling resistors R97 andR98 respectively. The devices 91 and 92 for introducing the delay may besimilar, but should not be identical, so that the twoears perceive thetone dif-' ferently due to the different amplitude responsecharacteristics of the two signals supplied to the earphones.

The essence of the invention resides in improving the auditory receptionof sounds derived from a single source as electrical signals in whichpairs of transmission channels have their inputs coupled to the sourceand in which at least one of the channels includes means to introducevariations in amplitude response in the sound transmitted thereby and inwhich a pair of earphones are coupled respectively to the outputs of thetransmission channels .are employed to translate the electrical signalsinto sound. The delay which is provided for in the several forms .of theinvention may be introduced by an artificial line or any other suitabledevice which produces substantial It'will be clearto those skilled inthe art that, in each of the embodiments, various types of tone andvolume .controls maybe employed in conjunction with the amplifiers andmixers, in addition to those shown. and

described.

Vhile we have shown and described particular embodiphase shift of thesignal, such that when superimposed on i a earphone received through thethird path.

anneal invention. We thereforedesire, by the following claims,

to include within the scope of our invention all such similar andmodified forms of the apparatus disclosed, by which substantially theresults of the invention may be obtained by the use of substantiallythesame or equivalent means. In some of the claims 'the word groun isused. This is intended to mean any point of fixed potential.

We claim:

1. Apparatus for improving the auditory receptionof sounds in the formof electrical signals derived from a single source, comprising areverberation apparatus coupled to the source, an amplifier coupled tothe output of the reverberation apparatus, an output transformer havinga primary winding connected to the output of the amplifier and having asecondary winding provided with a center tap, a pair of earphones eachhaving two ter minals, means connecting one terminal of each earphoneto'one terminal of the source, and means connecting the other terminalsof the earphones respectively to the end terminalsof the transformersecondary winding.

' 2' The combination of a single source of musical tone signals, apairof earphones, means for transmittinga signal derived from said source toeachof said earphones in opposite polarity, additional means fortransmitting a signal from the source to each of the earphones in thesame polarity, and means'for delayingthfe signal transmitted through oneof saidnansiniaing means. J

"3. Thecombinat'ion .ofa single source of musiealton e signals, a pairof earphones,l;mean's for tran'sm i'tting a. signal derived from saidsource to each of said earphones in opposite phasq additional means. fortransmitting a signal from the source to the earphones in the samephase, means for adding reverberative signals to the signal transmittedthrough one of said transmitting means, and means for'adju'sting therelative amplitudes of the signals supplied to the two earphones.

4. The combination of a single source of musical tone signals, a pair ofearphones, means for transmitting a signal derived from said source toeach of-said earphones in opposite polarity, additional means fortransmitting a signal from the source to each of the earphones in thesame polarity, and means for causing'a phase shift in the signalstransmitted through one of said transmitting means. h

5. Thecombination of a musical tone signal source, a pair of earphonescomprising a first earphone and a second earphone, means forming firstand second signal transmitting paths coupling the source to the firstearphone, means forming third and fourth signal transmitting pathscoupling the source to the second earphone, means inthe first signaltransmitting path to introduce delay with resultant variations inamplitude response the audio frequency spectrum and combined at'the,first earphone with the signal transmitted through the second path, andmeans included in the thirdsignal transmitting path to introduce aslightlydifferent delay with resultant different variations in'amplitude response in the audio frequency spectrum when the signal iscombined at the second earphone with the signal transmitted through thefourth path. v 6.. The combination set forth in claim 5 in which meansare provided to cause the signal at the first earphone received. throughthe first path to be of opposite polarity with respect to the polarityof the signal at the second 7.; The combination of a musical tonesignalj source, a pair of earphones comprising a first earphone and asecond earphone, means forming a first signal transmitting path couplingthe source to the first earphone, means formingja'second signaltransmitting path coupling the sourcetothe first earphone, means formingthird" nd fourth signal transmission paths coupling the source tothesecond earphone, means to cause the signal transmitted through thefirst and third paths to be received at the earphone in oppositepolarity, and means in the second and 'fourth signal transmitting pathsto introduce delay witl't resultant variations in amplitude responsewhen combined with the signals transmitted through the first and thirdpaths.

8; The combination of a single source of audio frequency' signals, apair of earphones, means for delaying the transmission of audiofrequency signals coupled between the source and one earphone, a secondmeans for delaying the transmission of audio frequency signals coupledbetween the source and the other earphone, and means coupling the sourceto both earphones, the two means for delaying the signals beingsufiiciently different to produce different frequency responsecharacteristics in the two earphones.

9. Apparatus for reproducing sound from a moving record comprising, apair of pickups cooperable with the same sound track on the record andspaced from one another in the direction of movement of the record, thespacing being sufiicient that the signal at one of the pickups will bedelayed with respect to the signal at the other pickup by an interval inthe order of seventy milliseconds, a pair of earphones, and meanscoupling each of the pickups to each of the earphones, the couplingmeans for one of the pickups including means for one of the pickupsincluding means to cause the signals therefrom to be received at theearphones in opposite polarity.

10. Apparatus for improving the auditory reception of sounds derivedfrom a single source, comprising a reverberation apparatus coupled tothe source, an amplifier coupled to the output of the reverberationapparatus, an output transformer having a primary winding connected tothe output of the amplifier and having a secondary winding provided witha center tap, a pair of electroacoustic transducers each having twoterminals and positioned that a listener can receive sound in each carfrom one of said transducers to the practical exclusion of sound fromthe other of said transducers, means connecting one terminal of each ofsaid transducers to one terminal of the source, and means connecting theother terminals of the transducers respectively to the end terminals ofthe transformer secondary winding.

11. The combination of a single source of musical tone signals, a pairof electroacoustic transducers positioned so that a listener can receivesound in each ear from one of said transducers to the practicalexclusion of sound from the other otsaid transducers, means fortransmitting a signal derived from said source to each of saidtransducers in opposite phase, additional means for transmitting asignal from the source to the transducers in the same phase, means foradding reverberation to the signal transmitted through one of saidtransmitting means, and means for adjusting the relative amplitudes ofthe signals supplied to the two transducers.

12. The combination of a single source of electrical musical tonesignals, a pair of electroacoustic transducers positioned so that alistener can receive sound in each car from one of said transducers tothe practical exclusion of sound from the other of said transducers,means for transmitting a signal derived from said source to each of saidtransducers in opposite polarity, additional means for transmitting asignal from the source to each of said transducers in the same polarity,and means for causing a substantial phase shift in the signalstransmitted through one of said transmitting means.

13. An apparatus for improving the auditory reception of sounds derivedfrom a source as a single electrical signal, comprising a pair of signaltransmission channels having their inputs coupled to the source, atleast one of said channels including reverberative means to introducevariations in frequency response in the sound signals transmittedthereby when combined with signals from the 8 4 source, a pair ofelcctroacoustic transducers positioned so that a listener may hear soundin one car predominantly from one of the transducers and in the othercar predominantly from the other of said transducers, means couplingboth transducers to the source, and means coupling the transducersrespectively to the outputs of the transmission channels.

14. An apparatus for improving the auditory reception of sounds derivedfrom a source as a single electrical signal, comprising a pair of signaltransmission channels having their input coupled to the source, at leastone of said channels including means to introduce a time delay in thetransmission of the signal of an order of seventy milliseconds, thercbyto cause variations in frequency response in the sound signalstransmitted thereby when combined with signals from the source, a pairof electroacoustic transducers positioned so that a listener may hearsound in one ear predominantly from one of the transducers and in theother car predominantly from the other of said transducers, meanscoupling both transducers to the source, and means coupling thetransducers respectively to the outputs of the transmission channels.

15. An apparatus for improving the auditory reception of sounds derivedfrom a source as a single electrical signal, comprising a pair of signaltransmission channels having their inputs coupled to the source, atleast one of said channels including means to introduce variations infrequency response in the sound signals transmitted thereby whencombined with signals from the source, a pair of electroacoustictransducers positioned so that a listener will hear sound in one earpredominantly from one of the transducers and in the other carpredominantly from the other of said transducers, a pair of meanscoupling both transducers to the output of one of the transmissionchannels, another pair of means coupling the transducers to the outputsof the other transmission channel, one of said pairs of coupling meanssupplying the signals to the transducers in the same polarity and theother pair of coupling means supplying signals to the transducers inopposite polarity for a substantial portion of the time that the signalis being transmitted.

16. An apparatus for improving the auditory reception of sound derivedfrom a single sound record, a pair of pickups spaced along the soundrecord a distance sufficient to introduce a delay in the order ofseventy milliseconds in the electrical sound signals from one pickuprelative to those from the other pickup, a pair of signal transmissionchannels having their inputs coupled to the pickups, respectively, apair of clectroacoustic transducers positioned so that a listener mayhear sound in one ear predominantly from one of the transducers and inthe other car predominantly from the other of said transducers, meanscoupling one pickup to the transducers in the same polarity and meanscoupling the other pickup to the transducers in opposed polarity.

17. An apparatus for improving the auditory reception of sounds derivedfrom a single source as electrical signals, comprising a pair of signaltransmission channels having their inputs coupled to the source, each ofsaid channels including reverberative means to introduce variations infrequency response in the sound signals transmitted thereby whencombined with signals from the source, a pair of electroacoustictransducers positioned so that a listener may hear sound in one earpredominantly from one of the transducers and in the other carpredominantly from the other of said transducers, means coupling bothtransducers to the source, and means coupling the transducersrespectively to the outputs of the transmission channels.

18. in combination with a primary single source of electrical musicalsound signals, time delay introducing means coupled to the primarysource and having its output constituting a secondary source of musicalsound signals, a pair of electroacoustic translating means, meanscoupling t e primary source to each translating means, means couplingthe secondary source to each translating means, and means to reverse thepolarity of the signals from one of the sources to supply such signalsin opposite polarity to the two electroacoustic translating means.

References Cited in the file of this patent 10 Snow Nov. 15, 1938Hammond Feb. 4, 1941 Begun Aug. 24, 1943 Hayes Apr. 29, 1947 Olson Jan.3, 1950 Boelens et a1 Dec. 28, 1954 Fine Aug. 2, 1955

